Pressed wines are an integral part of grape processing and vary in quality and quantity depending upon the handling and pressing practices. In white wine processing, the free run juice is separated from press juice and is fermented separately. Press wines are generally inferior to free run juice because of the extraction of harsh tannins from skins and seeds. In red wine processing, the crushed grapes with skins and seeds are fermented and the free run wine is separated and the residue is pressed to recover additional wine. This press wine becomes excessively harsh and is normally diverted to a distilling material which is eventually recovered as grape spirits. However, this diversion results in economic loss since a by-product of lower value is recovered in place of red wine.
It is a common knowledge that harshness of wines results from extraction of large molecular weight tannins associated with skins and seeds of grapes. These tannins are referred to as condensed tannins in general and procyanidins polymers in particular. These large tannin molecules impart significant astringency and bitterness to the wines.
Many classical approaches are available to reduce harsh tannins from wines but in general they are non-specific and create a side effect in treatment of wines. Gelatin or egg white fining of wines which is traditionally applied to reduce harsh tannins, is only suitable for marginal harshness while their use necessitates their removal from wines by other treatments. Anion exchange resins can be applied to reduce the harsh tannins, but the treatment is non-specific and results in extensive loss of fruitiness of wines and removes a part of wine acid which must be replenished. It would be extremely beneficial to reduce the tannin content of pressed wines to produce a palatable wine product which retain its desirable characteristics including its red color.